What's happening with you:

Well, there's no longer any doubt about it: you look pregnant. This is the first week of the second half of your pregnancy, and it may bring some cheerful congratulations from friends and strangers alike. Beware of eager hands reaching out to touch your belly and guesses about the gender based on how you're carrying your weight. When people start to notice you're pregnant, you'll get a flurry of attention!

The top of your uterus is likely just above your belly button and you've probably put on more weight in your abdomen by now. You might as well ditch the belts and any garment with a waistband that cuts across your (disappearing) waistline. As your belly grows you may find your abdomen is getting a bit itchy as well, which is a natural consequence of rapidly stretching skin.

But your uterus is not the only thing that's expanding: by now you have a significantly higher blood volume and your feet and legs may be swelling. Your body is retaining more water and producing more fluid these days, so you may also notice excess saliva and a general heaviness that brings on backaches and hip strain. On the bright side, you probably have the energy you need to take your new symptoms in stride!

Mood swings have likely leveled out by now, only to be replaced with a creeping anxiety about what lies ahead. After your second trimester ultrasound, your pregnancy seems much more real and labor feels much closer than it did a mere week ago. Try to relax and enjoy your relatively comfortable second trimester. Instead of fretting about what could go wrong or how challenging childbirth could be, use the resources around you to calm your fears and encourage a positive, realistic perspective.

What's happening with your baby:

A fetus at 21 weeks weighs about 10 ½ ounces and is 7 ¼ inches from crown to rump (which is 18cm, or the size of a banana). While baby has been breathing the amniotic fluid into her lungs for a little while, she now begins to work on her swallowing ability. By the ninth month, babies may swallow as much as 18 ounces of amniotic fluid in the span of 24 hours! All of this swallowing helps your baby to develop her digestive system, and the amniotic fluid may also provide some extra calories and nutrition to help her grow.

When she swallows the amniotic fluid, your baby's digestive tract will absorb the water and pass most waste through her intestines, to the placenta and into your blood stream so your kidneys can filter it out. But not all of the waste will make it through to your body: some amniotic fluid debris, lanugo and epithelial cells will build up in your baby's bowel, forming a substance called meconium. This sticky dark material will be your baby's first bowel movement, but since it doesn't contain any bacteria, it's completely sterile.

An ultrasound this week could show your baby sucking her thumb or maybe stroking her face, actions that have become more frequent by now. Her developing swallowing reflex is one reason for the thumb sucking, but the brain of a 21 week old fetus has matured enough for her to sense touch, as well. Between the taste buds that are sprouting on her tongue and the nerve endings that are springing to life all over her body, your baby's awareness and understanding of her environment is expanding quickly and she may want to test her relationship with the things around her. Don't be surprised if you feel some stronger kicks and punches in your belly and ribs these days!

Things to do this week:

Although you still have a few months to go, this is a good time to sign up for prenatal classes. Doctors and midwives may not be able to devote enough time to answer all of your questions, and clinical visits are typically more technical than conversational, anyway. Specific childbirth classes (like Lamaze and hypnobirthing) or more general prenatal classes provide a comfortable environment where you can ask any questions that come up between prenatal visits; starting the classes early can help you learn more about your pregnancy as well as your labor and delivery.

It's a good idea to sign up for the classes now because they tend to fill up fast, but don't start them too far ahead of your delivery. Try to time the classes so they finish a month or so before your due date, because there's a better chance you'll remember the skills and techniques and apply them more easily if you have learned them fairly recently. Also, don't expect that your friend's childbirth class will be the perfect choice for you, since there are many types of classes out there and they're all tailored to specific needs and preferences. Look around until you find the approach that fits with your expectations, lifestyle and birth plan.

Medical musts:

If you didn't go last week, you may be getting ready for your second trimester ultrasound and wondering whether or not you should find out the sex of the baby. While an ultrasound is by no means necessary at this point in a low-risk pregnancy, many doctors and midwives prefer to conduct one just to make sure that the baby is developing well. Most experts agree that ultrasound poses no risk to you or your baby, but if you have any concerns about the safety or accuracy of the test, speak with your caregiver about it.

There are other things to monitor that aren't covered by routine medical visits, aspects such as good nutrition and adequate vitamins. It may seem pretty easy to stay healthy -- take your prenatal vitamins and avoid junk food -- but ensuring your body and your baby are getting enough nutrition can be more difficult than it seems. Calcium is one of the important minerals that you may be lacking without realizing it, and that can put your baby's health at risk.

You require a lot of calcium during pregnancy (between 1200 and 1500 mg per day), and since food can interfere with calcium absorption, you'll need to make a good effort to take in enough of this mineral to help baby's skeletal system grow strong and to increase your chances of carrying him full-term. Many pregnant women find that as they begin to crave sugary or salty foods, they also start to dislike milk and foods that are rich in dairy. Don't worry too much about this aversion, since there are plenty of ways to add calcium to the menu without having to stomach a glass of milk. Drinking calcium-fortified juices, eating vegetables like broccoli and kale and cooking rice or oatmeal with skim milk instead of water are great ways to sneak more calcium into your diet.

Tips for your partner:

Now that the pregnancy is public knowledge, you may find that you're feeling left out and a little resentful of your partner's limelight. Overcome feelings of jealousy and invisibility before they cause a rift in your relationship by taking an active role in her daily activities. You can satisfy the protective urges that you might also be feeling by staying beside her as the pregnancy progresses: fend off pawing strangers, attend prenatal classes without being asked and help her commit to an exercise routine by doing it along with her when you can. By helping her to stay safe and healthy, you'll be an important influence on the pregnancy and on the life of your infant.

Pregnancy can be an opportunity to grow closer together, as long as you make an effort to understand what she's going through and accept that you have an important role to play, too. If you still feel like you've been denied access to an exclusive and important club, connect with those who are in your situation or have already gone through it. There are many forums, formal or informal, where you can chat with other parents-to-be who aren't carrying their child, and you'll find that some casual dialogue can really open up your perspective, provide encouragement and help you enjoy the pregnancy experience more.

This week's FAQs:

Since I'm at the halfway point in my pregnancy, should I have gained half my weight by now?

Weight gain during pregnancy is different for every woman, and it's difficult to say just how much you should gain by the end of your nine months. A 21 week fetus accounts for only a fraction of your weight, but your body needs extra blood, tissue and fat stores to support its growth. Are you carrying twins? Are you underweight or overweight? Are you short or tall? All of these can impact how much you should gain and how difficult it could be to maintain a healthy weight.

On the other hand, there are some widely used markers for various phases of pregnancy. For instance, most women should aim to gain between two and six pounds during the first trimester (though some will actually lose weight due to morning sickness), but begin to gain weight more rapidly (around a pound each week) when the second trimester rolls around. If your doctor has recommended that you gain around 25 or 30 pounds through the course of your pregnancy, you would want to have put on 10 or 12 pounds by now, or a little less than half your total pregnancy weight gain.

You should continue to gain about a pound a week from the beginning of your second trimester to the start of your ninth month, but if you've already put on more than half of what you had intended to gain by the end of your pregnancy, it may be time to consider your snacking rituals and your exercise routine. Also, beware of any sudden weight gain (more than 3 pounds in a week), which could signal a complication with the pregnancy.

I hate it when people try to touch my belly. How can I keep people out of my personal space?

Ah, the pregnant belly. If anything is a magnet for strange hands, it's the rounded abdomen of an expectant mother. But while others see it as cute and inviting, it's still your stomach and you probably wouldn't welcome a stranger patting you on the tummy before you became pregnant, so why should you now?

Fending off the belly rubs can be a tricky matter, especially if you want to preserve social decorum. First, use the resources around you. It may be impolite to snap at strangers who pat your tummy with the best of intentions, but it's not out of line to explain your distaste for belly touching to your friends and family. Let them intercept the reaching arms, and they can gently explain how that impulse makes a mom-to-be feel a little exposed and uncomfortable.

If you couldn't care less about manners, you can give them a taste of their own medicine: pat their belly back! And if you find that your patience is wearing thin, you can just come right out and tell them to stop. But remember that people aren't trying to harm you, they probably just want to share the experience and congratulate you. If you can get the message through in a nice way, do so.

How can I tell the difference between normal uterus discomfort and premature labor?

This is the point when odd abdominal discomforts begin to strike more frequently, and you may be worried about what they could mean. You'll probably experience some mild uterine contractions after certain activities, and these are nothing to worry about. Orgasm will cause your uterus to contract, but sex during pregnancy is perfectly safe for most women. Exercise can also lead to mild contractions: when you're working out, your body releases a chemical called norepinephrine that causes your muscles to contract, including your uterine muscles. In general, this contraction won't interfere with your pregnancy or lead to early labor.

Of course, any twinge in your lower abdomen will raise concern, so it's best to familiarize yourself with the symptoms of premature labor in order to catch any problems before they become serious. First, pay attention to how long the contractions last: if they continue after you stop exercising and you have more than four in an hour, you should call your doctor. The next big sign to watch out for is vaginal bleeding, since a pink or brownish discharge can indicate that your membranes are breaking and labor is imminent. Cramping, pelvic pressure, dull backache and stomach upset can also signal labor, so contact your caregiver at the first sign of trouble.

Helpful hint:

Since you have probably gained enough weight to warrant some bigger clothes and comfortable accessories, you may be drawn into the world of highly-specific pregnancy products. It's nice to start shopping when you're starting to show, but be careful not to splurge on gimmicky items. Examine specialized products closely, since you may find that a maternity/nursing shirt combo is not as practical or as comfortable as you had hoped.

Preparing for your little one can get expensive, and if you let your penchant for the adorable win out, you could wind up wasting your money. When it comes to baby, a few little extras are fine, but earmark most of your budget for good quality necessities and include the big ticket items on your baby registry so your close friends and family will know what to splurge on for your shower!